She doesn't wrap up EVERY loose end, but she wraps up enough of them.
I'm glad I had the experience of being part of the HP fan community when HBP came out, to join in with others speculating what might happen, re-reading and looking between the lines of all 6 books for hints of what might be coming in the last book.
When I first finished HBP, I was all "OMG, Snape is evil!!!" and then I read and reread between the lines and thought "hmm, maybe he's NOT evil afterall... but I can't be sure, and maybe it's all just wishful thinking and he really is a bad guy." You have the opportunity to read the last book right away and find out for certain, without having to wait two whole years to read the conclusion!
So it's up to you- do you want to find out how this ends, or do you want to let it all digest a while first and try to savor it longer? It's a shame the long HBP thread is no longer here- you'd be able to share in some of our theories that we came up with before reading the last book. (It got deleted for too many references to explicit fan fiction.) I don't know if any really old threads may still exist on other Harry Potter fan sites- it's just too easy to click the wrong thing and read book 7 spoilers.